1. Field of the Invention
The invention relates to a vehicle pneumatic tire, in particular for utility vehicles, with a carcass, with a belt built on radially outside the carcass, and with a profiled running strip built on the belt radially outside the belt, the belt being formed from at least three belt plies arranged so as to lie one on the other radially from the inside radially outward, the radially inner and the radially outer belt ply being working plies with parallel steel strengtheners embedded in rubber, the strengtheners of the radially inner working ply forming in their orientation an angle α to the circumferential direction U of 10°≦α≦45°, and the strengtheners of the radially outer working ply forming an angle γ to the circumferential direction U of 10°≦γ≦45°, and, as seen in the circumferential direction U of the vehicle tire, the strengtheners of one working ply having an opposite axial inclination direction to the strengtheners of the other working ply, and the belt ply arranged between these two working plies being a belt ply designed as zero-degree ply and having parallel strengtheners which are embedded in rubber and which form in their orientation an angle β to the circumferential direction U of 0°≦β≦5°.
2. Discussion of Background Information
Conventional utility vehicle pneumatic tires usually have a four-ply belt with what is known as a triangular configuration, in which two working plies are arranged one on the other in the radial direction and their steel cords have in each case an approximately 15° to 30° to the circumferential direction, the steel cords of one working ply and those of the second working ply being inclined in a different axial direction A. The working plies thereby form a crossbracing. In belts of this type, beneath the working plies a belt ply is usually located which is designed as a blocking ply and the steel cords of which have an angle of 45° to 60° to the circumferential direction, with the result that the cords of the working plies and of the blocking ply form a triangular bracing. In addition, above the two working plies is usually formed an additional protective ply which forms the fourth belt ply and the steel cords of which likewise have an angle of approximately 15° to 30° to the circumferential direction of the vehicle tire. Belts of this type have restricted circumferential rigidity. The movability of the belt margins which is thereby made possible may have an adverse effect upon the durability of the tire. Furthermore, the belt may experience radial expansions during operation. This growth may lead to excessive and uneven abrasion of the tire.
It is also known to design utility vehicle pneumatic tires with a four-ply arrangement, with a radially inner blocking ply having steel cords which form an angle of approximately 45° to 65° to the circumferential direction, with two working plies which are formed above the blocking ply and conventionally form a crossbracing of their steel cords, with an orientation of the steel cords of approximately 15° to 30° in each case, and with a fourth belt ply which is formed on the outer working ply radially outside the two working plies and which is designed as what is known as a 0° ply, its strengtheners made from steel cords being oriented essentially in a circumferential direction with an angle of 0° to 2.5° to the circumferential direction. In such constructions, the circumferential rigidity of the belt is increased, this having a positive effect upon the durability of the belt. However, the influence of the 0° ply is restricted essentially to the radially outer working ply. However, the inner working ply is designed with residual movability, again having adverse influences upon durability and abrasion.
Furthermore, occasionally, a design of a utility vehicle pneumatic tire with a belt arrangement in which a 0° ply is formed radially between the two working plies has been proposed. In these proposed designs, the two working plies are still forming with crossbracing and their steel cords are oriented in each case at angles of approximately 18° to the circumferential direction. This design, admittedly, makes it possible to have high circumferential rigidity and, as compared with a conventional utility vehicle pneumatic tire, improved durability and an improved abrasion pattern. The steel cords of these known working plies are usually steel cords of the type 3×0.20+6×0.35 NT. So that these steel cords, which have a breaking force F of 1700 N and an extension under 10% of the breaking force of less than 0.15%, acquire sufficient puncture resistance, a multiplicity of steel cords of a relatively thin cross section are formed in a high arrangement density in the working plies. Steel cords with a large cross-sectional thickness, which would be beneficial to belt durability, can therefore be used to only a limited extent. Even if they were used, the high arrangement density necessary to limit the puncture risk would entail a high belt ply weight, large quantities of material and an adverse influence upon abrasion.